The above photo depicts Bradypodion thamnobates, a South African species, tucked under the snow.
Temperature is another hotly debated topic among hobbyists. On the one hand, many species do come from parts of the world that are considered tropical. On the other hand, the particular biotopes they occupy can differ significantly from what we tend to think of as "tropical". For instance, the equator runs through central Kenya--where lowland forests and plains are paradigmatically "tropical". However, many of our prized species come from high altitude areas that can see very cool temperatures, especially at night. Indeed, several species regularly see frost and/or snow. Things get even more complicated when we take into account that most species have evolved to experience a significant drop in nighttime temperature. Whereas daytime temperatures may approach 30C (86F), nighttime temps can fall well below 10C (50F).
As it turns out, many species--including commonly kept species such as panthers and veileds--do quite well with daytime temperatures in the 23-25c (73-77f) range. This meshes nicely with room temperature in most of our houses. If provided 2-4 hours with a warm basking area where they can see temps around 28c (82f), your veiled or panther chameleon will be happy. Species that hail from higher altitudes or areas outside the tropical zone such as Jackson's, would be happier with room temps around 20-23C (68-73F), and a basking temp of 28C (82F) max. As we add to the site, details about specific species' preferences will be added.
This is where a great many keepers go wrong. When products such as nighttime heat lamps and infrared and/or ceramic heaters have a chameleon featured on the label, it is a small wonder that new keepers think they need to provide some source of heat at night. As mentioned, many chameleons have evolved to experience a significant nighttime temperature drop. Indeed, it is theorized the the health of some species such as Jackson's will slowly deteriorate and eventually fail if nighttime temperatures are too high. The theory is that they cannot get proper rest when nighttime temps are above a certain threshold. To be sure, there are some exceptions (e.g. some of the low-land species from Cameroon), but panther and veiled chameleons are not among these. For panther and veiled chameleons, nighttime temperatures in the 15-17C (59-62F) should be the considered the upper limit. For montane species, such as Jackson's, nighttime temperatures above 15C (59F) may become problematic. I drop all my chameleons--panthers, veileds, jackson's, and newborns--down to 10C (50F) every night possible. In short, most chameleons need a good nighttime drop to get proper rest. Nighttime heat lamps, or heaters can negatively affect the health of your chameleon--especially if they emit light (chameleons need absolute darkness to sleep).
Female Veiled Chameleons
Huge egg clutches (>50) in female veiled chameleons is such a problem, that this section is necessary. According to most experts, this phenomenon is due to two main factors: over-feeding and temperature. The same is probably true for most egg-laying females, but veileds appear to suffer the most here. For female veiled chameleons, please keep the ambient temperatures slightly lower, ~21C (70F), and basking temperatures should never exceed 27C (80F). Egg binding and early death is a real problem for these beautiful females, so please feed sparingly, and keep them cooler. Nighttime temps can safely drop below 15C (59F), and should not exceed 17C (62F).